After filling the gas tank, the gas guage needle will fall to empty. Then, sometimes, the needle will slowly move to full, or fall back to "E" or move up to "F" immediately and fall back to "E". The needle continues to behave in this manner for a few gallons.
After a few miles (gallons used), the needle will usually, but not always, work normal.
I use the trip miles now after filling the tank just to make sure I do not run out of gas (good back up plan).
What might be the problem(s)? What is/are the solutions?